As solar batteries, there are photoelectric conversion devices including a light-absorbing layer composed of a compound semiconductor. As such a compound semiconductor, a chalcopyrite-based compound semiconductor made of CIGS or the like is used. In this photoelectric conversion device, for example, a first electrode layer composed of Mo is formed on a substrate composed of soda-lime glass, and a light-absorbing layer composed of a compound semiconductor is formed on this first electrode layer. Further, a transparent second electrode layer composed of ZnO or the like is formed on the light-absorbing layer through a buffer layer composed of ZnS, CdS or the like.
As the production method for forming a compound semiconductor constituting such a light-absorbing layer, there is used the method using a vacuum device, such as a sputtering method. However, manufacturing cost is high in the method using a vacuum device, and thus various production methods are under development for the purpose of cost reduction in place of the above-mentioned high-cost production method.
For example, U.S. Pat. No. 7,341,917 discloses the technology of obtaining a compound semiconductor by application of a feedstock solution. In the U.S. Pat. No. 7,341,917, first, a metal chalcogenide such as Cu2S is dissolved in hydrazine (N2H4) to form a hydrazinium-based precursor solution. After that, this solution is applied onto the electrode layer to form a coat, and then this coat is heat treated, to thereby obtain a metal chalcogenide film (compound semiconductor layer).
Unfortunately, in the method for producing a compound semiconductor as described in the U.S. Pat. No. 7,341,917, the dissolved feedstock concentration is limited to approximately 1% by mass, and the solution for forming a coat has a low viscosity. This makes it difficult to form a good coat of approximately several μm on an electrode layer by a simple method such as the blade process. Therefore, the feedstock solution needs to be applied several times for obtaining a compound semiconductor having a desired thickness, which complicates the steps. Further, as a result of the formation of a compound semiconductor by application of a feedstock solution several times, the heat-treated state differs in the respective layers, and accordingly a stress is apt to be generated between the layers to cause cracks in the compound semiconductor.
In view of the above, the production method capable of producing a compound semiconductor having a desired thickness well easily is desired.